All power semiconductor devices include an active region in which the active elements of the device are found. The active region of a typical power semiconductor device includes a diffusion of one conductivity type formed in a semiconductive body of an opposite conductivity type thereby forming a PN junction. A power semiconductor device is more susceptible to breakdown at the periphery of the PN junction of the active region where there is crowding by the electric field lines (i.e. where the radius of curvature of the diffusion that forms the PN junction is low). Thus, in high voltage semiconductor power devices, a termination feature is included to spread the high electric fields at the periphery of the PN junction of the active area to reduce the strength of the electric field in order to improve the ability of the device to withstand breakdown.
A well known termination feature used in power semiconductor devices is a field ring surrounding the active region. A field ring is a diffusion of a conductivity type opposite to that of the conductivity type of the semiconductive body in which it is formed. To effectively reduce the field strength around the edge of the PN junction in the active region the distance between the field ring and the edge of the active region may be selected to obtain a desired potential drop between the PN junction of the active region and the field ring. Typically, by reducing the distance between the active region and the field ring, the field strength around the edge of the active region may be reduced. However, it should be noted that the selected distance must be such that it does not cause the field strength to become too high at the edge of the field ring itself. Thus, the distance between the field ring and the junction in the active region is a factor that increases the size of the device.
It is also well known to use a plurality of spaced field rings to spread the electric field. However, the spacing between the field rings disadvantageously consumes a large area around the active region of the semiconductor device thereby increasing the size of the device.